U.S. Pat. No. 5,526,777 discloses a cleaning arrangement for the combustion air of an internal combustion engine of a portable handheld work apparatus wherein a blower of the portable handheld work apparatus moves air to an air filter. The air filter is accommodated in a filter housing and partitions the filter housing into a contaminant space and a clean space. A carburetor of the engine is fluidly connected to the clean space of the filter housing. The air filter can be charged with dust to an extreme extent in dependence upon the dirt content of the ambient air of the portable handheld work apparatus. During operation of the cleaning arrangement, increasing flow resistances of the air filter develop in dependence upon the layer thickness of the dust deposited on the air filter. The operation of the engine can be thereby affected. The cleaning arrangement requires correspondingly high maintenance.
It is an object of the invention to provide a cleaning arrangement for the combustion air of an internal combustion engine which ensures a disturbance-free operation of the engine over long services times.
The cleaning arrangement of the invention is for the combustion air of an internal combustion engine including an internal combustion engine of a portable handheld work apparatus. The engine includes a carburetor and the cleaning arrangement includes: a filter housing defining an interior; an air filter mounted in the filter housing for filtering the combustion air supplied to the engine; the air filter being mounted in the filter housing so as to partition the interior into a contaminant space and a clean space fluidly connected to the carburetor; a blower for moving a flow of the combustion air laden with dust to the filter housing; a centrifugal-force separator mounted in the contaminant space for receiving the flow of combustion air and for dividing the flow into a central core flow having a low particle density of the dust and a tangential flow surrounding the core flow with the tangential flow having a particle density of the dust greater than the low particle density; and, the centrifugal-force separator having conducting means for conducting the central core flow into the contaminant space.
According to the invention, the cleaning arrangement is provided with a centrifugal-force separator with which dust-laden combustion air is supplied under an overpressure by the blower to the centrifugal-force separator during operation. A central core flow having a low particle density and a tangential flow of larger particle density than in the core flow forms in the centrifugal-force separator. The tangential flow surrounds the core flow. After axial passage of the core flow through the centrifugal-force separator, the core flow exits into the contaminant space of the filter housing in which the centrifugal-force separator is integrated.
The filter housing has a partition plane which partitions the filter housing into first and second filter housing parts. It is advantageous to so mount the centrifugal-force separator in the filter housing that it is essentially partitioned in the partition plane of the filter housing. For maintenance and cleaning purposes, the centrifugal-force separator is also opened when the filter is opened in order to do maintenance work.
To simplify the manufacture of the filter housing and of the centrifugal-force separator, it is practical to form at least one part of the centrifugal-force separator as one piece with the filter housing. It can also be practical to configure the centrifugal-force separator as a separate component in one or several parts and to form-tightly connect the separator to the filter housing so that it can be separated. Preferably, the centrifugal-force separator has a partition plane which partitions the same in the longitudinal direction. The partition plane lies in the longitudinal axis of the centrifugal-force separator or is parallel to its axis.
The feed by the blower of the combustion air to be cleaned takes place preferably via a feed channel to the centrifugal-force separator. The feed channel is formed in the first filter housing part. The second filter housing part is connected seal tight to the first filter housing part during operation of the portable handheld work apparatus and this second part preferably accommodates the air filter and a part of the centrifugal-force separator. The core flow in the centrifugal-force separator is characterized by a low particle density and, during operation of the cleaning arrangement, the core flow is taken out via a dip tube arranged at a first axial end of the centrifugal-force separator. The core flow is conducted out of the centrifugal-force separator via the dip tube in an essentially axial direction. It is practical to completely fix the dip tube to the first filter housing part.
It is practical to expand the dip tube diffusor-like or with a funnel shape to the contaminant space of the filter housing in dependence upon the space available in the filter housing and the desired flow guidance of the core flow. Preferably, the feed channel opens tangentially into the centrifugal-force separator at a second axial end thereof lying opposite to the first axial end. The feed channel is guided upstream over a part length about the casing of the centrifugal-force separator. The feed channel preferably tapers toward its entry opening into the centrifugal-force separator.
It is practical to configure the centrifugal-force separator as a cyclone or axial cyclone. Other configurations of centrifugal-force separators, such as a turbofilter, can also be used.
A cooling air fan of the engine is preferably suitable as a blower for feeding uncleaned combustion air into the centrifugal-force separator. It can be practical to conduct away the tangential flow into the cooling air flow via the engine housing.